Method for manufacturing a shadow mask

Abstract

A method for manufacturing a shadow mask is used for color television picture tubes and the like. The surface of a shadow mask body, made of Fe-Ni type alloy, is ion-nitriding processed so as to make the most of the low thermal expansion property inherent in the alloy. The result is that the color purity degradation caused by the thermal expansion at temperature increases of the mask, and by the resonance of the mask itself, can be prevented, thereby realizing a shadow mask serving to render a highly refined CRT.

What is claimed is: 
     
       1. A method for manufacturing a shadow mask, comprising the steps of: (a) annealing, at a predetermined temperature, a shadow mask body which is composed by forming a number of apertures in a metallic plate made of Fe-Ni type alloy;   (b) press-molding the annealed shadow mask body;   (c) ion-nitriding a surface of the press-molded shadow mask body; and   (d) performing a blackening process on the ion-nitrided shadow mask body, wherein said ion-nitriding step is carried out at a temperature predetermined based upon at least one of retention time, processing pressure, processing atmosphere, and melanism-processing temperature.   
     
     
       2. The method for manufacturing a shadow mask of claim 1, wherein the metallic plate is made of one of Fe-Ni(36%) alloy and an invar alloy, and has a thickness of less than 0.15 mm. 
     
     
       3. The method for manufacturing a shadow mask of claim 1, wherein said annealing step is carried out at a predetermined temperature of approximately 1150° C. in vacuum atmosphere. 
     
     
       4. The method for manufacturing a shadow mask of claim 1, wherein said step of performing a blackening process is carried out at a temperature of approximately 600° C. in one of steam atmosphere and gas atmosphere. 
     
     
       5. The method for manufacturing a shadow mask of claim 1, wherein said ion-nitriding step is carried out at a temperature of approximately 420° C. 
     
     
       6. The method for manufacturing a shadow mask of claim 1, wherein said ion-nitriding step is carried out at a predetermined temperature within a range of 350° C.-500° C.